linux-kernel - Re: [RFC PATCH v1 0/4] virtio/vsock: some updates for MSG

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Date:   Mon, 26 Jun 2023 18:30:23 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...rdevices.ru, oxffffaa@...il.com
Subject: Re: [RFC PATCH v1 0/4] virtio/vsock: some updates for MSG_PEEK flag

On Sun, Jun 18, 2023 at 09:24:47AM +0300, Arseniy Krasnov wrote:
>Hello,
>
>This patchset does several things around MSG_PEEK flag support. In
>general words it reworks MSG_PEEK test and adds support for this flag
>in SOCK_SEQPACKET logic. Here is per-patch description:
>
>1) This is cosmetic change for SOCK_STREAM implementation of MSG_PEEK:
>   1) I think there is no need of "safe" mode walk here as there is no
>      "unlink" of skbs inside loop (it is MSG_PEEK mode - we don't change
>      queue).
>   2) Nested while loop is removed: in case of MSG_PEEK we just walk
>      over skbs and copy data from each one. I guess this nested loop
>      even didn't behave as loop - it always executed just for single
>      iteration.
>
>2) This adds MSG_PEEK support for SOCK_SEQPACKET. It could be implemented
>   be reworking MSG_PEEK callback for SOCK_STREAM to support SOCK_SEQPACKET
>   also, but I think it will be more simple and clear from potential
>   bugs to implemented it as separate function thus not mixing logics
>   for both types of socket. So I've added it as dedicated function.
>
>3) This is reworked MSG_PEEK test for SOCK_STREAM. Previous version just
>   sent single byte, then tried to read it with MSG_PEEK flag, then read
>   it in normal way. New version is more complex: now sender uses buffer
>   instead of single byte and this buffer is initialized with random
>   values. Receiver tests several things:
>   1) Read empty socket with MSG_PEEK flag.
>   2) Read part of buffer with MSG_PEEK flag.
>   3) Read whole buffer with MSG_PEEK flag, then checks that it is same
>      as buffer from 2) (limited by size of buffer from 2) of course).
>   4) Read whole buffer without any flags, then checks that is is same
>      as buffer from 3).
>
>4) This is MSG_PEEK test for SOCK_SEQPACKET. It works in the same way
>   as for SOCK_STREAM, except it also checks combination of MSG_TRUNC
>   and MSG_PEEK.
>
>Head is:
>https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d20dd0ea14072e8a90ff864b2c1603bd68920b4b

Nice cleanup, LGTM, but I'd like a comment from Bobby.

Thanks,
Stefano